On Monday Casteel, 43, was arrested in connection with a shooting that took place on the Interstate 96 outside of Detroit on Oct. 18. According to prosecutors he is expected to face more charges in the other jurisdictions over the 24 shootings that terrorized a four county area of Michigan since mid-October.

"We had so many people who were so afraid to travel down 96, parents pulling their kids out of school. So, for us it was a very big challenge to go out here and find this guy," Lt. Mike Shaw of the Michigan State Police said.

Casteel was arrested after a raid on his home in Wixom, Mich. During the raid police seized two handguns which they believe Casteel used to pump bullet holes in two dozen vehicles during the terror spree.

Police told ABCNews.com that re-interviewing their witnesses ultimately led to their big break. One of the drivers, who was uninjured, gave a description of the shooter's car, and was able to identify part of the license plate. The driver also noticed a logo for Michigan State University – Casteel's alma matter-- on the car.

"We did some follow up on interviews with some old witnesses that kind of pointed us in the right direction," Shaw said. "We used some good old fashion police work to go ahead and find a lead for us to get this guy."

Authorities said that Casteel had a license to carry a pistol in Kentucky, but not in Michigan.

Casteel is being held on $2 million bail after being charged. It is unclear if he entered a plea. He is charged with six counts for the shooting in Livingston County, including three counts of felony firearms, one count of assault with a dangerous weapon, one count of assault with a dangerous weapon with unlawful intent, and one count of discharging from a vehicle.

Only one person was hit during the string of shootings across a 100-mile stretch of roads in Oakland, Livingston, Ingham and Shiawassee counties. That victim was seen on surveillance footage limping into a gas station with a bullet wound to the buttocks, looking for help.

Raulie Casteel Arrested: Motive Still a Mystery

The motive still remains a mystery and many wonder why a Michigan State graduate who had worked in environmental sciences as a geologist, according to The Associated Press, would allegedly fire at passing motorists.

Casteel's relatives talk of mental problems that he suffered. His mother, Lana Hunt, told the Detroit Free Press that she worried he was mentally ill, but that he refused to get help, while Casteel's aunt told the Detroit News that he was paranoid that the government was after him.

"There was some statements made by family members with respect to his mental health and we're looking into that as well," Livingston County Prosecutor David Morris said Wednesday.

Secret Service chief psychologist Dr. Marisa Randazzo told "Good Morning America" that Casteel told his mother that if anything happens to him, the government may be involved. She said that this kind of paranoid thought can be a clue as to what may have been motivating him.

"There's so much we don't know about this case and that we're learning as this investigation unfolds," she said. "But we've got two big clues with what the mother and his aunt shared with newspapers, about this paranoia, about 'if anything happens to me, the government is to blame.' This suggests he may have been experiencing what we call a break with reality, which may have been part of a developing mental disorder like a psychosis."

Randazzo said that most people who develop this type of mental disorder don't engage in violence. Under stress -- like dire financial conditions, loss of a job -- people can develop this break with reality at some point.

"What's critical here is that law enforcement or the criminal justice system can play a key role in getting someone like this into treatment and back on track. These are treatable conditions," she said.